1. Field of the Invention
The present invention relates to oil well sealing units, and more particularly for sealing units deployable below ground to reduce pump height.
2. Description of the Prior Art
In the recent past, significant efforts have been directed to increase the economies and efficiency of oil well pumps and to reduce the physical structure thereof both for the sake of visual impact and in the interests of costs. Typically an oil well or any other well where liquids are pumped from subterrainian deposits entail long strings sucker rods which necessarily must be articulated above ground to achieve pumping. In each instance a reciprocal motion of the sucker rod is entailed and it is the length of the stroke that heretofore has yielded the best returns in economy. The longer pumping stroke, however, entails higher elevation at which the reciprocal force is applied to the rod strength or, alternatively, deeper deployments of below ground seals; the first alternative entailing large supporting structures and the second alternative demanding complex lifting mechanisms to bring the seal to the surface for periodic maintenance. Thus, for example, in U.S. Pat. No. 3,640,342 to Robert H. Gault, issued Feb. 8, 1972, a travelling stuffing box has been devised which is particularly suitable for below ground sealing. Concurrently in my patent application Ser. No. 824,346 filed Aug. 15, 1977 I have found that certain beneficial aspects can be realized by the use of non-linear arrangements for counterbalanced pumping systems which, however, lose part of the efficiency realized to the losses entailed of drawing the sucker rods through the seal packing. In addition, since secondary recovery is now widely practiced throughout the United States, exposure of the downhole seal to hot steam or abrasive particles entails a more frequent interval for seal maintenance and any techniques which extend the life of the packing or the maintenance period greatly enhance the cost effectiveness of the low profile pumps, particularly when the long stroke lifting hoists are entailed in the maintenance schedule.
Packing, while suitable for its purpose, entails intimate contact with the sucker rod over large areas and thus presents a large frictional loss in the course of pumping. Thus the benefits achieved in oscillatory pumping systems are often, at least in part, reduced by the friction of the packing. Furthermore, packing as originally envisioned is best suited for ground surface installation and is best maintained thereat. The maintenance sequences envisioned originally for packing accommodates the lack of scraping action which, in the case of well fluids carrying abrasives often results in destruction of the polished rods or other close tolerance structures.